When party crashers started a fight with the parent of a friend at a high school graduation party in May 2010, Muema moved quickly to intervene. In the next instant, he was on the floor, the left side of his face bloody and throbbing.

An unseen assailant had come from behind to strike Muema with a bat.

In the heat of that moment, Muema wanted to get to his feet and retaliate, but a friend pulled him up and told him, “We need to get you to a hospital.”

Muema would soon understand that with that one blow of a bat, the one thing he most dreamed about in life — playing college football — was in jeopardy.

The record-breaking running back out of Charter Oak High in Covina was only two months from beginning a new life as a freshman at San Diego State, but doctors were telling him that the damage to his left eye might never allow him to play contact sports again.

Muema’s injuries required 36 stitches, his orbital bone was fractured, and when the vision in his left eye began to deteriorate it was discovered he had a macular hole in the retina of his eye.

“I was panic-stricken,” said Trina Powell, Muema’s aunt and legal guardian. “The love of his life was football, and to hear doctors say he would never play football again? But I told Adam, ‘Are you going to trust in them or trust in God?’

“It was traumatic for him, but it was such a humbling experience.”

Two years later Muema, 20, is among a committee of talented running backs at San Diego State trying to replace Ronnie Hillman, who is now in the NFL. Muema, the soft-spoken redshirt sophomore who is truly a young man of few words, said of the life-changing bat incident, “I’ve learned to stay away from the stupid stuff. There were a lot better things ahead for me. I’m thankful for the opportunities I have.”

Powell and Muema’s coaches said he always was the kid with an incredible resolve. They had to kick him out of the weight room in high school because he stayed so long, and on the field there was almost a frightening single-mindedness to his running.

The longtime head coach at Charter Oak, Lou Farrar, cherishes a picture he has in his office of Muema flying like Superman above a string of lineman. He’s gripping the tip of the football, extending it over the goal line to score the winning touchdown in a playoff game.

“He goes for the goal line like no kid I’ve given the ball to in 44 years,” Farrar said. “I just love the kid. He doesn’t quit — ever. What he did in some high school games … I’m serious, he made some kids decide they didn’t want to play football anymore.”

It was that drive that got Muema through the grueling rehab of his eye injury. Doctors performed surgery to place a gas bubble behind Muema’s eye to allow the hole to heal. For two weeks, 23 hours a day, Muema had to keep his head down to allow the bubble to stay in place.

On an apparatus similar to a massage table with a cushion to hold his head, Muema watched television and played Guitar Hero using a specially designed mirror. He ate that way, slept that way. And for the one-hour of reprieve? “I still kept my head down,” he recalled with a smile.

“I was ready to come (to San Diego State), so I was doing what I had to do.”

The rehab stint was almost harder on the other important people in Muema’s life as they waited to know his fate in football.

“When the fight happened, it just broke my heart,” Farrar said. “He’s had so many hurdles to get over. He didn’t need this to start out with at San Diego State.”

Early in his life, around the age of 2, Muema’s mother could no longer care for him. She had six children, and when she was deemed legally unfit to have them, Trina Powell, the sister of Adam’s mother, and her husband accepted Adam into their family.

Among five kids, Muema shared a bunk bed with his cousin, A.J. Powell, now a junior wide receiver at Portland State. The two played, competed and fought like brothers. Trina Powell said they acted like twins.

Muema still has contact with his birth mother, but he calls Powell his “mom.”

“It’s like he’s my own,” said Powell, who attends all of Muema’s Aztecs home games. “I don’t know life without Adam in it. All my kids are named with an ‘a’ and so is Adam. It’s like he was a gift given to me.”

Powell gave Adam the opportunity to play all sports — he could switch-hit in baseball — but football was his passion from the time he was 5. He was clumsy off the field, Powell recalled with laughter, and in his very first carry in flag football, he ran the opposite direction, realized it just before he reached the goal line, and then ran past everyone in the opposite direction for the score.

“If he ever makes it big, I’m releasing that tape!” Powell said. “From that day on I knew nobody was ever going to be able to catch him. You could see he was different from the other kids. It was always the ‘Adam Show.’ ”

Muema led Charter Oak to two CIF Southeast Division championships and rushed for 4,552 yards and scored 61 touchdowns in his career. He set the Chargers’ record of touchdowns in a season (29) and a game (four, twice).

Once at SDSU, Muema redshirted his first year in 2010, and last year he shared backup duties with Walter Kazee behind Hillman, the star who left school early and was drafted in the third round by the Denver Broncos.

Kazee, a senior coming off a knee injury suffered in the ninth game last season, is a jitterbug back who has averaged 4.5 yards per carry in his career and has nine touchdowns. Muema has averaged 6.0 yards per carry and scored three touchdowns.

Of course, Muema’s average was padded with a spectacular run against Boise State late last season. From his own 19-yard line, Muema bounced left, burst between two defenders, and was gone, sprinting 81 yards for a touchdown. Muema had his best game against the Mountain West champs, running for 119 yards and two TDs, while also catching a score.

“He’s really strong and he’s really fast,” Aztecs head coach Rocky Long said of Muema.

If they can both stay healthy, Muema and Kazee can be expected to share the bulk of the running workload this season for Long, who doesn’t want to expose himself to the fates with one star tailback.

Of the philosophy, Muema said, “If you perform, you should play. That’s up to the coaches. I’m feeling good. It’s time to step up and win a championship.”

From afar in Covina, Charter Oak coach Lou Farrar will be watching intently.